Previous version compared the pad's output binary passed mulaw-slinear
conversion and frequency conversion with the prepared "good result".
In such case, a test may fail when the implemantation changes. In fact,
the frequency conversion algorithm was changed in isaki-audio2, so
output waveforms is not completely the same (but that's no problem with
the audio waveforms).
New version uses slinear_le/2ch/44100Hz input data and compares the
output binary with the input data. pad with no conversions should
output the same binary.
Fix PR kern/54187.
e0eeaafc81